Dealkylation of n-alkyl aromatic amines

ABSTRACT

Aromatic amines mono-substituted on the amino nitrogen atom with a non-aromatic hydrocarbon substituent such as N-ethyl aniline are converted to primary aromatic amines by removal of the nonaromatic hydrocarbon substituent at a temperature of 275*-400*C in the presence of an aluminum anilide catalyst.

United States Patent 1 Napolitano [451 Sept. 18,1973

l l DEALKYLATION OF N-ALKYL AROMATIC AMINES [76] Inventor: John P. Napolltano, 2444 Clawson,

Royal Oak, Mich. 48073 [22] Filed: Feb. 14, 1969 [21] Appl. No.1 799,522

[56] References Cited UNITED STATES PATENTS 2,762,845 9/1956 Stroh et al. 260/578 2,814,646 11/1957 Kolka ct a1. 2601578 X 3,275,690 9/1966 Stroh et al. 260/578 X 3,394,190 7/1968 Wall ct a1. 260/578 X FOREIGN PATENTS OR APPLICATIONS 846,226 8/1960 Great Britain 260/578 OTHER PUBLICATIONS Chambers, et al., Journal Organic Chemistry", V01. 28, pages 3144-3147, 1963 Primary Examiner-Robert V. Hines AttorneyDonald L. Johnson [57] ABSTRACT Aromatic amines mono-substituted on the amino nitrogen atom with a non-aromatic hydrocarbon substituent such as N-ethyl aniline are converted to primary aromatic amines by removal of the non-aromatic hydrocarbon substituent at a temperature of 275-400C in the presence of an aluminum anilide catalyst.

6 Claims, No Drawings benzopyrone,

DEALKYLATION OF N-ALKYL AROMATIC AMINES BACKGROUND SUMMARY It is an object of this invention to provide a process for removing non-aromatic N-substituent groups from a N-substituted aromatic amine. The process involves heating the N-substituted aromatic amine to a temperature of from about 275400C. in the presence of an aluminum anilide catalyst,

DESCRIPTION OF THE PREFERRED EMBODIMENTS The above and other objects are accomplished by providing a process for removing a non-aromatic hydrocarbon substituent from an N-substituted aromatic secondary amine forming a primary amine, said process comprising heating an aromatic amine having the formula:

ANH-R,

wherein R, is selected from the group consisting of alkyl radicals having two-l2 carbon atoms, cycloalkyl' radicals having six-l2 carbon atoms and alpha-' branched benzyl radicals having 8-20 carbon atoms, and A is an aromatic group, to a temperature offrom 275-400C. in the presence of an aluminum anilide catalyst.

The secondary aromatic amines which may be used include both monoand polynuclear aromatic amines. Also, the aryl portion may be fused with other cyclic systems including heterocyclic systems such as those containing oxygen, nitrogen orsulfur. By way of exam-' ple, A in Formula I may be derived from benzene, naphthalene, anthracene, phenanthrene, indene, isoindene, benzofuran, isobenzofuran, thionaphthene, indole, isoindole, indolenine, 2-isobenzazole, 1,2- benzodiazole, l,3-benzodiazole, indiazine, 1,3-

benzoisodiazole, 1,2,3-benzotriazole, benzisoxazole, benzoxadiazole, l,2-benzopyran, 1,4-benzopyran, 1,2- quinoline, isoquinoline, l ,3- benzodiazine, 1,2-benzisoxazine, acenaphthene, fluorene, dibenzopyrrole, xanthene, thianthrene, phenothiazine, phenoxazine, naphthacene, chrysene, pyrene, triphenylene, and the like.

The aromatic group may also be substituted with other radicals as long as they do not interfere with the course of the reaction. Some further examples of these include 3-methylphenyl, 4-methylphenyl, 2-tertbutylphenyl, 2,6-di-ethylphenyl, p-chlorophenyl, pmethoxyphenyl, p-ethoxyphenyl, p-butoxyphenyl, 3,5- dichlorophenyl, 3,5-dibromophenyl, p-seceicosylphenyl, a-naphthyl, B-naphthyl, 4-chloro-a- N-cyclohexyl-a-naphthylamine,

2 naphthyl, 4-methyl-a-naphthyl, 4-tert-butyl-a-' naphthyl, p-pentacontylphenyl, 2-(a-methylbcnzyl) phenyl, and the like.

Alkyl radicals represented by R in Formula I which may be substituted on the nitrogen to form the secondary amines include ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-amyl. isoamyl, sec-amyl, tertamyl, n-decyl, isodecyl, sec-decyl, tert-decyl, ndodecyl, sec-dodecyl, and the like. Useful cycloalkyl radicals are cyclohexyl, cyclooctyl, 4-tert-butylcyclohexyl, 4-sec-hexylcyclohexyl, and the like. Useful alpha-branched benzyl groups include a-methylbenzyl, a,a-dimethylbenzyl, a-ethyl-benzyl, a-methyl-4-tertbutylbenzyl, a-methyl-4-sec-dodecyl-benzyl, a-methyl-2,3-benzobenzyl, and the like. It is apparent from the foregoing what aromatic secondary amines can be used in the process. By way of further example, suitable amines include N- ethylaniline, N-ethyl-Z-ethylaniline, N-n-propyla'niline, N-n-propyl-2-ethylaniline, N-cyclo-hexylaniline,

N-n-dodecyl-ptoluidine, N-cyclooctyI-p pentacontylaniline, N-(4- tert butyl-cyclohexyl)-p-chloroaniline, N-(amethylbenzyl)-3,5-dibromo-aniline, N-(a,a-dim ethyl- 4-sec-nonylbenzyl)aniline, N-cyclohexyl-2- cyclohexylaniline, N-cyclohexyl-4-cyclohexylaniline, N-ethyl-7-aminoindene, N-n-butyl-7-amino-4,6- dibromoindene, N-ethyl-4-aminobenzofuran, N-n-propyl-4-aminobiphenyl, N-n-octyl-p-anisidine, N-cyclohexyl-7-aminoindole, N-ethyl-7-amino-4- nitroisobenzofuran, N-(a-methylbenzyl)-4-amino-7- acetoxyindolenine, N-ethyl-7-amino-4- methoxyisothionaphthene, N-cyclooctyl-4 aminobenzoisoxazole, N-(4-sec-hexylcyclohexyl)-7- amino-4 iodobenzoisoxazole, N-sec-butyl-6- aminocoumarin, N-ethyl-6-amino-8-fluorocoumarin, N-ethyl-6,8-dichloro-B-naphthylamine, N-ethyl-4- nitro-a-naphthylamine, N-ethyl-6-aminoquinoline, N- n-dodecyl-4-aminoacenaphthene, N-cyclohexyl-4- amino-7-methylacenaphthene, N-ethyl-7-aminoquinazoline, N-n-propyl-7-aminoquinoxaline, N-secoctyl-7-amino-phthalazine, N-ethyl-l-aminofluorene, N-n-dodecyl-4-sec-amyl-2-aminofluorene, N- cyclohexyl-2-an1ino-6,8-difluorofluorene, -N-ethyI-aaminoanthracene, N-n-butyl-a-amino-4- phenylanthracene, N-cyclooctyl-B-amino-4-(2,4-disec-heptylphenyl)anthracene, N-(3,5- diisopropylcyclohexyl)-B-aminoanthracene, N-nhexyl-B-aminQ-phenanthrene, .N-n-decyl-3-amino-8- ethoxyphenanthrene, N-ethyl-2-amino-7- chlorophenanthrene, N-(a-methylbenzyl)-laminoxanthene, N-ethyl-Z-aminophenazine, N-ethyl-laminonaphthacene, N-ethyl-2-aminochrysene, N-n-hexyll -aminochrysene, N-ethyI-Z-aminopyrene, and N-cyclooctyl-Z-aminotriphenylene.

The aluminum anilide catalyst can be such that the anilide groups are the same as the aromatic amine or they may be different. They are readily prepared by reacting aluminum turnings or granular aluminum with an aromatic primary or secondary amine at a temperature from about l25-200C. Hydrogen evolves and an aluminum anilide type catalyst forms.

The catalyst can also be made by reacting an aluminum alkyl such as triethyl aluminum with a primary or secondary aromatic amine. Care should be taken to avoid contact with oxygen since many aluminum alkyls are pyrophoric.

The amount of catalyst can vary over a wide range. In general, good results are obtained when there is enough catalyst in the reaction mixture to provide one gram atom of aluminum for each 5-25 gram moles of aromatic amine. A preferred range is 1 gram atom of aluminum for each 7.5-20 gram moles of aromatic amine.

Although the process is applicable for the removal of alkyl, cycloalkyl and alpha-branched benzyl groups, it will hereafter be referred to as dealkylation" for the sake of simplicity. The dealkylation proceeds at a temperature of 275-400C. The rate increases at higher temperatures, so it is preferred to operate the process in a range of from about 300-400C.

The N-substituent defined above is such that it is capable of forming olefinic unsaturation at the carbon atom bonded to the amino nitrogen. For example, an n-butyl radical can form l-butene. The cyclohexyl radical can form cyclohexene and the a-methylbenzyl radical can form styrene. These same olefinic hydrocarbons are known to cause nuclear alkylation of aromatic amines (U.S. Pat. No. 2,814,646), so in order to obtain good yields of dealkylated product it is important that no additional olefin be present beyond that evolved by the dealkylation reaction.

In a more preferred embodiment of the invention the evolved olefin is removed from the reaction zone as it forms. Since the dealkylation temperatures are above the boiling point of many of the aromatic amines, it is not always possible to merely allow the evolved olefinic hydrocarbon to vaporize out of the reaction zone at atmospheric pressures without at the same time vaporizing the N-substituted aromatic amine or the dealkylated aromatic amine product. In order to avoid this and at the same time effect the removal of a substantial portion of the evolved olefinic hydrocarbon, the process is preferably operated under a pressure of from about l-100 psig above the normal vapor pressure of the dealkylated primary amine product at whatever particular temperature the dealkylation is being conducted. The pressure can be readily controlled in this range by first determining the vapor pressure of the desired primary amine product in the temperature range at which the dealkylation would be carried out and then providing a controlled vent of the vapor phase during the actual dealkylation so that the pressure remains from about l-100 psig above the vapor pressure exhibited by the primary amine product. In other words, if a prior test showed that at a temperature of, say, 350C. the amine product alone would exhibit a pressure of, say, 200 psig, then when a de-alkylation is carried out at 350C. to obtain such product the pressure should be controlled in the region of from about 201-300 psig. The vent gas removed can be conducted through a condenser whereby any amine values carried out with the vent gas can be recovered.

In a' similar embodiment, the dealkylation isconducted in such a manner that the evolved olefin is removed from the reaction zone at a controlled rate such that the partial pressure of olefin in the dealkylation vessel remains within the range of from about 1-100 psig. In this manner, the yield of dealkylated primary amine is maximized. i

The manner in which the dealkylation process is conducted is readily understood from the following examples. All parts are by weight unless otherwise stated.

EXAMPLE 1 In a reaction vessel provided with a stirrer, heating means, condenser and a nitrogen atmosphere was placed 306 parts of N-ethylaniline and 4.5 parts of, aluminum turnings. While stirring, this was heated to reflux and refluxed for 1.5 hours. It was then cooled and transferred under a nitrogen atmosphere to a pressure reaction vessel. An additional 306 parts of N- ethylaniline were added and the pressure vessel sealed. Heating and stirring were commenced. After 30 minutes, the temperature was 208C. and the pressure still 0 psig. At 25 minutes the temperature was 240C. and the pressure only 10 psig. After 35 minutes the temperature reached 296C. and the pressure rose sharply to psig, indicating the start of dealkylation accompanied by ethylene formation. At 45 minutes the temperature was 330C. and the pressure psig. The temperature was maintained at 330C. for 4 hours, during which time the pressure rose to 510 psig. The vessel was then cooled to 25C. and the residual pressure of 230 psig vented. A 15 per cent conversion of aniline was recovered by distillation.

EXAMPLE 2 In the pressure reaction vessel of Example 1 place 242 parts of N-ethylaniline and 5.4 parts of granular aluminum. Heat to 200C. and stir for 30 minutes. Cool and vent. Seal the vessel and heat to 350C. As the pressure rises to 200 psig vent the gas phase at a controlled rate so that the pressure remains in a range from 200-250 psig. When no further venting is required to hold the pressure, cool the reaction to 25C. and discharge the vessel contents. Combine this with the liquid condensed out of the vent gas and wash with a 25 per cent aqueous sodium hydroxide solution followed by two washings with a saturated sodium chloride solution. Distill the product to recover aniline in high conversion.

Other N-substituted anilines can be dealkylated following the general procedure of Example 2. For instance, N-n-propyl-aniline, N-n-butylaniline, N-tertbutylaniline, N-isoamylaniline, N-tert-octylaniline, N- sec-decylaniline, N-cyclohexylaniline, N-(4-tertbutycyclohexyl)aniline, N-(4-sec-hexylcyclohexyl)- aniline, N-(a-methylbenzyl)aniline, N-(a,a-dimethylbenzyl)-aniline, N-(a-methyl-4-sec-dodecylbenzyl)aniline, N-(a,a-dimethyl-4-tert-octylbenzyl)aniline, and the like, will dealkylate under the above general conditions to form aniline.

EXAMPLE 3 trogen andthenseal and heat to 375C. When the pres- .sure reaches .75 psig begin a controlled vent of the v.apor phase through a condenser system and thereby maintain the pressure at 75 psig. After 6 hours, cool the reaction mixture to 50C. and wash with 25 per cent aqueous caustic. Wash again with saturated sodium chloride solution and then distill the product at 50 mm Hg. to recover a-naphthylamine.

EXAMPLE 4 The dealkylation of Example 3 is repeated except a pressure vessel is not used and the reaction is conducted at reflux under atmospheric pressure. The a-naphthylamine is recovered in the same manner.

EXAMPLE 5 In a reaction vessel fitted with a stirrer and heating means and provided with a nitrogen atmosphere place mole parts of N-(a-methylbenzyD-B- naphthylamine. Over a 1 hour period, at 75-100C., add a per cent solution of one mole part of triethyl aluminum. Continue heating up to about 290C., allowing the toluene solvent and evolved styrene to distill out. Continue heating at 290C. for 8 hours and then cool to 50C. Hydrolyze and extract the aluminum with a per cent aqueous caustic solution. Wash twice with saturated sodium chloride solution and then dry over anhydrous magnesium sulfate. Distill the product at reduced pressure to recover B-naphthylamine.

EXAMPLE 6 In the reaction vessel of Example 5 place 10 mole parts of N-cyclohexyl-3-aminophenanthrene. Over a one hour period at 75-100C., add one mole part of triethyl aluminum as a 20 per cent solution in toluene. Heat the mixture to 350C, allowing the toluene and evolved cyclohexene to distill out. Continue heating for 6 hours and then wash the product at 100C. with a 25 per cent aqueous caustic solution, followed by a saturated sodium chloride solution. Distill the product at reduced pressure to recover 3-aminophenanthrene.

As mentioned earlier, aromatic amines having an unsubstituted ortho position can be alkylated in this ortho position by reaction with an olefin in the presence of an aluminum anilide catalyst, as shown in U.S. Pat. No. 2,8l4,646. This process works best using ethylene as the olefin and is slower with olefins such as propylene or isobutylene, which give secondary or tertiary radicals. As stated in U.S. Pat. No. 2,814,646, the process works at a very high rate when the aromatic nitrogen atom is substituted. The present process makes possible the formation of orthosecondary or tertiary alkyl substituted aromatic amines at a high rate. This is accomplished by alkylating an N-substituted aromatic amine as defined by Formula I in which at least one position on said aromatic group ortho to the amino nitrogen atom is unsubstituted except for hydrogen, with a secondary or tertiary alkyl radical forming olefin such as propylene, butene or isobutylene using the process of U.S. Pat. No. 2,814,646, and then, by means of the present process, removing the N-substituent. This embodiment of the invention is illustrated by the following example.

EXAMPLE 7 7.5 Mole parts of N-ethylaniline is reacted with one mole part of granular aluminum at 200C. to form an aluminum anilide catalyst. Following this, the mixture is reacted with propylene at a pressure of 500 psig at 260C. for a 2 hour period, forming N-ethyl-2- isopropyl aniline in high yield. Excess propylene is vented off at a controlled rate through a condenser system until aniline-derived materials begin to condense. This will occur around 150 psig. The resultant mixture is heated up to 375C. and the pressure controlled by gradual venting in a manner such that no substantial amount of aniline-derived material distills out. This will require allowing the pressure to climb to about 250 psig. After 4 hours at 375C. the reaction mixtureis cooled, washed with a 25 per cent aqueous caustic solution, and then distilled to give o-isopropylaniline in good yield.

The above general procedure can be followed in intro-ducing other secondary or tertiary groups into the aromatic nucleus. For example, to prepare o-tertbutylaniline, the N-ethylaniline is first alkylated with isobutylene, followed by dealkylation of the ethyl group.

Another feature of this invention is that it makes possible the production of mono-orthoalkylated aromatic amines without coproducing substantial amounts of dialkylated aromatic amines. For example, 0- ethylaniline is a valuable intermediate for the production of indole by the process of U.S. Pat. No. 2,409,676. The prior art methods of alkylating aniline give mixtures of o-ethylaniline and 2,6-diethylaniline. The present process makes possible almost the exclusive production of o-ethylaniline. This is accomplished by first reacting ethylene with N-ethyl-aniline using an aluminum anilide catalyst. This gives almost exclusively N-ethyl-Z-ethylaniline. The N-ethyl group can then be removed employing the present process, giving a high conversion of o-ethylaniline. The following example Ethylene is reacted with 10 mole parts of N- isopropylaniline at 250C. in the presence of one mole part of aluminum anilide under 800 psig of ethylene pressure. After 1 hour, the unreacted ethylene is slowly vented through a condenser system until a substantial amount of aniline-derived material begins to form in the condenser. This occurs around psig. The mixture is then heated to 350C. and the pressure controlled by venting evolved propylene through the condenser system in such a manner that only a small amount of aniline-derived material escapes. This will require allowing the pressure to rise to about 250 psig. After 4 hours at 350C. the mixture is cooled, washed with 25 per cent caustic, and then distilled to give 0- ethylaniline in high yield.

The aromatic amines made by this process are wellknown compounds and are useful in a large variety of applications. For example, they can be used as intermediates in the manufacture of dyes, insecticides or herbicides. They can also be used as antioxidants or antiozonants in rubber. Many are also effective antiknock agents for gasoline.

I claim:

1. A process for removing an alkyl, cycloalkyl or benzyl substituent from an N-alkyl, cycloalkyl or benzyl aniline forming a primary aniline, said process comprising heating an aniline having the formula:

wherein R, is selected from the group consisting of alkyl radicals having two-l2 carbon atoms, cycloalkyl radicals having six-l2 carbon atoms and a-methyl. and a,a-dimethylbenzyl radicals, and A is a phenyl group, to a temperature of from 275-400C. in the presence of an aluminum anilide catalyst and no additional olefin beyond that evolved by the dealkylation.

7 8 2. The process of claim 1 wherein R, is the ethyl ture. S P- 5. The process of claim 4 wherein R is the ethyl 3. The process of claim 1 wherein R, [S the isopropyl group group.

4. The process of claim I conducted at a pressure of 5 The process of clam 4 wherem the Sopropyl from about ll00 psig above the normal vapor prespsure of said primary aniline at the reaction tempera- UNITED STATES PATENT 0mm CERTIFICATE OF CORRECTION ptember 18, 1973 Pam No. 5 159,997 Dated fim enmrgl) John P. Napolitano It is certified that error appears in the above-identified patent and that said Letters Patent are hexeby corrected as shown below:

T- In the heading on patent insert Y Assignee: Ethyl Corporation, Richmond, Virginia Signed and sealed this 1st day of January 19 714..

(SEAL) Attest:

EDWARD M.FLETGI ER,JR'. 1 3 RENE D. TEGTMEYER A Attestingv Officer" a I v Acting Commissioner. of Patents 

2. The process of claim 1 wherein R1 is the ethyl group.
 3. The process of claim 1 wherein R1 is the isopropyl group.
 4. The process of claim 1 conducted at a pressure of from about 1-100 psig above the normal vapor pressure of said primary aniline at the reaction temperature.
 5. The process of claim 4 wherein R1 is the ethyl group.
 6. The process of claim 4 wherein R1 is the isopropyl group. 